Java线程池

　　java.util.concurrent.Executors是Java提供的一个线程池工具类，通过该工具类，我们可以创建出不同类型的线程池。

　　从这个工具类的api来看，Java提供了五种线程池，分别是：

• FixedThreadPool
• WorkStealingPool
• SingleThreadExecutor
• CachedThreadPool
• ScheduledThreadPool

FixedThreadPool

package java.util.concurrent;

public class Executors {

    public static ExecutorService newFixedThreadPool(int nThreads) {
        return new ThreadPoolExecutor(nThreads, nThreads, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>());
    }public static ExecutorService newFixedThreadPool(int nThreads, ThreadFactory threadFactory) {
        return new ThreadPoolExecutor(nThreads, nThreads, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>(), threadFactory);
    }

}

线程池的属性：

• 核心线程数：创建线程池实例时指定（必需）
• 最大线程数：与核心线程数一致
• 空闲线程的存活时间：默认是0，没有限制
• 存活时间单位：默认是纳秒
• 线程工厂：可在创建线程池实例时指定（可选），默认默认Executors.defaultThreadFactory()
• 任务队列：LinkedBlockingQueue

　　
WorkStealingPool

package java.util.concurrent;

public class Executors {public static ExecutorService newWorkStealingPool(int parallelism) {
        return new ForkJoinPool(parallelism, ForkJoinPool.defaultForkJoinWorkerThreadFactory, null, true);
    }

    public static ExecutorService newWorkStealingPool() {
        return new ForkJoinPool(Runtime.getRuntime().availableProcessors(), ForkJoinPool.defaultForkJoinWorkerThreadFactory, null, true);
    }

}

SingleThreadExecutor

package java.util.concurrent;

public class Executors {public static ExecutorService newSingleThreadExecutor() {
        return new FinalizableDelegatedExecutorService(new ThreadPoolExecutor(1, 1, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>()));
    }

    public static ExecutorService newSingleThreadExecutor(ThreadFactory threadFactory) {
        return new FinalizableDelegatedExecutorService(new ThreadPoolExecutor(1, 1, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>(), threadFactory));
    }

}

线程池属性：

• 核心线程数：1
• 最大线程数：1
• 空闲线程的存活时间：默认是0，没有限制
• 存活时间单位：默认是纳秒
• 任务队列：LinkedBlockingQueue
• 线程工厂：默认Executors.defaultThreadFactory()

CachedThreadPool

package java.util.concurrent;

public class Executors {public static ExecutorService newCachedThreadPool() {
        return new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60L, TimeUnit.SECONDS, new SynchronousQueue<Runnable>());
    }

    public static ExecutorService newCachedThreadPool(ThreadFactory threadFactory) {
        return new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60L, TimeUnit.SECONDS, new SynchronousQueue<Runnable>(), threadFactory);
    }

}

线程池属性：

• 核心线程数：0
• 最大线程数：Integer.MAX_VALUE
• 空闲线程的存活时间：默认是60
• 存活时间单位：默认是秒
• 任务队列：SynchronousQueue
• 线程工厂：默认Executors.defaultThreadFactory()

ScheduledThreadPool

package java.util.concurrent;

public class Executors {public static ScheduledExecutorService newSingleThreadScheduledExecutor() {
        return new DelegatedScheduledExecutorService(new ScheduledThreadPoolExecutor(1));
    }

    public static ScheduledExecutorService newSingleThreadScheduledExecutor(ThreadFactory threadFactory) {
        return new DelegatedScheduledExecutorService(new ScheduledThreadPoolExecutor(1, threadFactory));
    }

    public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) {
        return new ScheduledThreadPoolExecutor(corePoolSize);
    }

    public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize, ThreadFactory threadFactory) {
        return new ScheduledThreadPoolExecutor(corePoolSize, threadFactory);
    }

}

线程池属性：

• 核心线程数：创建线程池实例时指定（必需）
• 最大线程数：Integer.MAX_VALUE
• 空闲线程的存活时间：默认是0，没有限制
• 存活时间单位：默认是纳秒
• 任务队列：DelayedWorkQueue
• 线程工厂：默认Executors.defaultThreadFactory()